[Cryptography] When your security is too secure

[Jon Callas]

> On Nov 24, 2025, at 22:52, Peter Gutmann <pgut001 at cs.auckland.ac.nz> wrote:
> 
> 
> I think most diaries are like this as well, no-one is ever going to read
> hundreds of pages of notes on someone else's life, particularly if they're
> written in barely-legible scrawl, unless it's the biographer of someone
> famous.  So probably most diaries will default to the Lincoln's-letter effect,
> especially if it's written journal-style where it just records the major
> happenings of the day for future reference by the author.  And in that case A
>> C (I irrelevant), because you want a record of what happened last October
> but don't really care who knows that was when you bought a new laptop.

Sure, and I also have two relevant examples.

The first is Samuel Pepys. Pepys kept his diary and used various mechanisms to hide what he was writing a little. He describes his own sexual indiscretions often using non-English words, and wrote primarily in Thomas Shelton's "tachygraphy" shorthand. It's presumed that his primary adversarial threat was that of keeping affairs secret from his wife, as well as some of the documentation of petty corruption (which he participated in). At the same time, he sent the diaries off to be preserved after his death, and it's only relatively recent that full, unexpurgated texts have been published. He both wanted some confidentiality, and at the same time wanted them all preserved for posterity.

The second is the diaries of Anne Lister, who is called "the first modern lesbian" which used her own code, again, particularly for the steamy bits. She called it "crypthand." One of her family, John Lister, decoded them and then re-buried them because he was gay and really didn't want anyone looking closely at the sexuality of the Lister family. They were again decoded and published by Helena Whitbread quite recently (volume 2 came out in 2020). 

It seems that Pepys wanted the diaries read once all the people were safely dead. He took trouble to preserve them. In the case of Lister's diary, it is more interesting because on the one hand she wanted to keep them secret, and on the other hand she's detailed!

The relevance to this discussion to me is that I think that particularly in Lister's case, the primary audience is Lister herself, and she'd have been heartbroken if they had lost Availability (like if they burned in a fire). To me, even when a diarist is hoping the diaries will die with them, A is more important than C -- meaning that they'd prefer someone else read them than they lose access to them, themselves.

	Jon